feat: Implement lightweight UDP interactive UI for Neovim

- Rewrote gemini-ui.lua to send native Neovim prompt selections, Ghost Text diff accept/reject actions, and smart context highlighting directly to the backend via zero-latency UDP port 3002, entirely replacing the old xecute_agent terminal subprocesses.
- Added prompt_user and preview_diff extmark lua functions for non-destructive diff review.
- Updated the Rust backend mcp-memory-server UDP listener to ingest the new gent_ask and interactive schema payloads and route them to the EventBus.
- Updated README.md and instructions.md with UDP documentation.

server/src/main.rs

@@ -247,6 +247,17 @@ async fn run_server(state: Arc<MemoryState>) -> Result<(), Box<dyn std::error::E
                                 };
                                 let _ = nvim_udp_state.handler.state.event_bus_tx.send(event);
                         }
+
+                        // 4. Interactive Agent UI Events
+                        if payload.event.starts_with("agent_") {
+                            let topic = format!("nvim:ui:{}", payload.event);
+                            let event = crate::state::GenericEvent {
+                                topic,
+                                session_id: Some(payload.session_id.clone()),
+                                payload: serde_json::json!(&payload),
+                            };
+                            let _ = nvim_udp_state.handler.state.event_bus_tx.send(event);
+                        }
                 }
             }
         }